A seatback structure for a vehicle seat provided with a pivotable upper seatback support is known. See JP2010-42748A and JP2013-23065A, for instance. Typically, the seatback includes a seatback lower support having a lower end attached to a rear end part of a seat cushion (typically via a reclining mechanism), and a seatback upper support having a lower end pivotally attached to an upper end of the seatback lower support. A drive mechanism is incorporated in the seatback for actuating the seatback upper support relative to the seatback lower support.
In the seatback structure disclosed in JP2010-42748A, a motor mount plate extends between a pair of side members of the lower seatback support to support an electric motor, and a nut and screw mechanism is provided in association with a pivot mechanism provided between the upper seatback support and the lower seatback support. A wire and pulley mechanism transmits the power of the electric motor to the nut and screw mechanism.
JP2013-23065A discloses a similar seatback structure. The power of an electric motor provided in the lower seatback support is transmitted to a nut and screw mechanism for tilting the upper seatback support relative to the lower seatback support via a torsional flexible cable.
As such a conventional seatback structure includes various component parts over a large area of the seatback, some care is required to avoid interference between moveable component parts of the drive mechanism with the pad of the seatback. Also, the drive mechanism including a transmission mechanism occupies a relative large space, and this complicates the seatback design.